In general, an image sensor is a device for converting an optical image into an electrical signal. Image sensors are generally classified as charge coupled devices (CCDs) or complementary metal oxide silicon (CMOS) image sensors (CISs).
The CCD has disadvantages, such as a complex driving method and high power consumption. Also, the CCD is manufactured through a multi-step photolithography process; it needs a very complicated manufacturing process. Therefore, the CIS is currently in the spotlight as a next-generation image sensor to resolve the disadvantages of the CCD.
The CIS includes a photodiode and a MOS transistor in a unit pixel to sequentially detect an electric signal in each unit pixel using a switching method for displaying an image.
FIG. 1 is a sectional view of a related art CIS.
In the related art CIS, a device isolation layer 63 is formed on a substrate 61, and then a gate 65 is formed on the substrate 61 with a gate insulation layer 64 interposed therebetween.
Next, a low-concentration N− ion implantation region 69 is formed at one side of the gate 65. Spacers 70 are formed on both sidewalls of the gate 65. Then, a high-concentration N+ ion implantation region 72 is formed at the other side of the gate 65.
However, according to the related art CIS, since an N− diffusion region (i.e., a photodiode region) is included in an interface of the device isolation layer 63, a portion of the lattice structure collapsed from the trench etching process performed to form the device isolation layer 63 serves as an interface electro trap and a junction leakage. Therefore, the related art CIS has a problem of weak to low illumination.
Additionally, according to the related art CIS, the device isolation 63 between pixels may not appropriately function and cause a problem of crosstalk where light of one pixel is transmitted into other pixels. Especially, according to the related art CIS, since the depth of a trench in the device isolation layer 63 is within 0.5 μm, electrons generated from the light of a long wavelength (especially, red) may not be efficiently isolated.